Add pytest suite and Gitea Actions CI/CD pipeline

83 tests (94% coverage of src/py) covering the builder pipeline
(gallery sync, HTML/CSS generation, image processing, full site
build) and the Flask webui (routes, uploads, theme/font management).

Dockerfile gains a `test` stage (pytest) between the wheel builder
and the prod image, and pins the alpine base to a full patch tag so
Renovate can classify updates. CI workflow builds, smoke-tests, runs
the suite, scans with Trivy, and publishes/releases on merge to main,
following the same pipeline already running on adguard-cidre.

tests/test_builder_utils.py

@@ -0,0 +1,93 @@
+from pathlib import Path
+
+from src.py.builder import utils
+
+
+def test_load_yaml_missing_file_returns_empty_dict(tmp_path, caplog):
+    result = utils.load_yaml(tmp_path / "missing.yaml")
+    assert result == {}
+
+
+def test_load_yaml_parses_existing_file(tmp_path):
+    path = tmp_path / "data.yaml"
+    path.write_text("foo: bar\nnum: 1\n", encoding="utf-8")
+    assert utils.load_yaml(path) == {"foo": "bar", "num": 1}
+
+
+def test_load_theme_config_success(tmp_path):
+    themes_dir = tmp_path / "themes"
+    theme_dir = themes_dir / "modern"
+    theme_dir.mkdir(parents=True)
+    (theme_dir / "theme.yaml").write_text("colors:\n  primary: '#000'\n", encoding="utf-8")
+
+    theme_vars, returned_dir = utils.load_theme_config("modern", themes_dir)
+
+    assert theme_vars == {"colors": {"primary": "#000"}}
+    assert returned_dir == theme_dir
+
+
+def test_load_theme_config_missing_raises(tmp_path):
+    themes_dir = tmp_path / "themes"
+    try:
+        utils.load_theme_config("missing", themes_dir)
+        assert False, "expected FileNotFoundError"
+    except FileNotFoundError:
+        pass
+
+
+def test_clear_dir_creates_missing_dir(tmp_path):
+    target = tmp_path / "out"
+    utils.clear_dir(target)
+    assert target.is_dir()
+    assert list(target.iterdir()) == []
+
+
+def test_clear_dir_removes_existing_content(tmp_path):
+    target = tmp_path / "out"
+    target.mkdir()
+    (target / "file.txt").write_text("x", encoding="utf-8")
+    sub = target / "sub"
+    sub.mkdir()
+    (sub / "nested.txt").write_text("y", encoding="utf-8")
+
+    utils.clear_dir(target)
+
+    assert target.is_dir()
+    assert list(target.iterdir()) == []
+
+
+def test_ensure_dir_creates_and_clears(tmp_path):
+    target = tmp_path / "out"
+    utils.ensure_dir(target)
+    assert target.is_dir()
+
+    (target / "stale.txt").write_text("x", encoding="utf-8")
+    utils.ensure_dir(target)
+    assert list(target.iterdir()) == []
+
+
+def test_copy_assets_copies_existing_folders(tmp_path):
+    js_dir = tmp_path / "js"
+    style_dir = tmp_path / "style"
+    build_dir = tmp_path / "output"
+    js_dir.mkdir()
+    style_dir.mkdir()
+    (js_dir / "app.js").write_text("console.log(1)", encoding="utf-8")
+    (style_dir / "style.css").write_text("body{}", encoding="utf-8")
+
+    utils.copy_assets(js_dir, style_dir, build_dir)
+
+    assert (build_dir / "js" / "app.js").exists()
+    assert (build_dir / "style" / "style.css").exists()
+
+
+def test_copy_assets_skips_missing_folder(tmp_path, caplog):
+    js_dir = tmp_path / "missing_js"
+    style_dir = tmp_path / "style"
+    style_dir.mkdir()
+    build_dir = tmp_path / "output"
+
+    utils.copy_assets(js_dir, style_dir, build_dir)
+
+    assert not (build_dir / "missing_js").exists()
+    assert (build_dir / "style").exists()